Thrust and Pressure Class 9 Physics

Hello dear students, in this part we are going to discuss about the thrust and pressure. Try to answer the following questions, why the edges of knives and blade, tip of pins should be made sharp? Though the bit of drilling machines isn’t pointed till it manages to drill the holes in thick wall, how is it possible? The water stored in tank on terrace of building can be easily flow through tap in bathroom, but if tank is kept at ground will it flow? Here the answers of this entire question are related to the terms known as thrust and pressure. So let’s learn it with the help of following examples.

Take a brick and a tray containing sand; keep the tray on the table. Now keep the brick in horizontal position on tray and push it downwards and pick is slowly, so that it can penetrate through sand and leaves some mark. Now measure the margin created by brick into sand as x1. Now change the position of brick to vertical do the same and mark the depth of sand as x2. What do you observe? x1= x2 or not? Definitely you will find that the distances x1 and x2 are different. Why does it happen? It’s due the fact that, we had pushed with same force but of different surface areas. In horizontal position, area of brick facing sand is more, whereas in vertical position area of that brick on sand is smaller. Hence the brick penetrates more in vertical position than in horizontal position. i.e. though the applied push is same but the impact is different if the cross section is different. The push what we exerted is termed as thrust and the impact of it on sand known as pressure.Hence the thrust is the force acting on the object by means of push.

The thrust acting per unit area is known as pressure.

Hence, pressure= thrust/ area

Or, Pressure=force/ area

P = F/A

Si unit of pressure is newton per metre (N/m2) and CGS unit is dyne/cm2

N/m2 is also called as pascal (Pa)

Pressure is inversely proportional to Area.

There are so many day to day examples where the concept of pressure can be easily understood.

  1. If you are sick and doctor suggested taking injection, then the needle attached to syringe should be very sharp otherwise doctor has to apply tremendous thrust so as to inject the medicine in your vein. Just imagine this horrible situation!
  2. The knives used for cutting the veggies should be sharp enough otherwise we need to spend more energy to cut all of those veggies.
  3. If the tyres of your cycles are flat, it would be very difficult to run a cycle over the road; due to increase in area of tyre needs more force to run it.
  4. The point of nail should be sharp enough so that it can penetrate into wall with help of hammer.

Go through the following numerical to understand more about pressure.

Ex:1) Brick kept vertically on sand has area of 25 cm2, needs force of 120 N to insert into sand by 5cm. Find the pressure exerted on the sand surface.

Ex:2) Boy of mass 30 kg standing on the trampoline of area 2 m2, jump on it. Find the pressure acts on the surface on trampoline.

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